A: DMC transfer: EIS DMC CAPT/3 OR F/O/3 (DMC 3 -----> DMC 1 or 2)
 B: PFD ND transfer
 C: ECAM 1 (upper) DU to ECAM 2 (lower) DU
 D: ECAM ND transfer: ECAM/ND1 or ECAM/ND2 (lower ECAM DU/ND1 or 2)
 (a) DMC transfer In the event of DMC1 (or DMC2) failure, the Captain (or First Officer) can switch over to DMC3. This is controlled by means of the EIS DMC selector switch (CAPT/3 or F/O/3 position). In this case, the DMC3 totally replaces the DMC1 (or 2) through the stage of the output switching relay of the failed DMC. The DMC3 acts as a back up (hot spare). In case of selection of the DMC3, the master DSDL and the feedback DSDL buses are switched in the DMC1 (or 2) output switching stage.
 NOTE : In the event of DMC failure, the DUs driven by this DMC
____ display a diagonal line, which helps the crew in making immediately the right action.
 (b) PFD-ND transfer
 1 PFD failure
_ In case of detected failure of the DU normally displaying the PFD image, there is an automatic PFD-ND transfer. The PFD image is presented on the DU normally showing an ND image. This transfer is automatically controlled by means of a discrete signal generated by the DMC upon recognition of the failure. This transfer can also be obtained manually by the pilot, by either of the two following means:
 -either deactivate the PFD by setting its potentiometer to OFF: this automatically transfers the PFD image on the ND, the ND image is then replaced by the PFD image
 - or press the PFD/ND XFR pushbutton switch, cross-changes the
 images between the PFD and ND. At each action on this pushbutton switch, there is an inversion between the 2 images: the one which was displayed on the left DU is displayed on the right DU and vice versa.
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 2_ ND failure
 In case of failure of the DU normally showing the ND image,
 the pilot can recover the display of the ND image on the
 remaining DU, normally showing the PFD image, by means of the
 PFD/ND XFR pushbutton switch.

 (c) ECAM DU failure In the event of upper ECAM DU failure, the Engine/Warning image is displayed on the lower ECAM DU instead of the system page or status message. This switching is automatic: upon reception of the upper DU anomaly signal, through the feedback DSDL bus, the DMC2 ECAM channel processor switches to an ECAM "single display" configuration which privileges the E/W processing. The lower ECAM DU receives the E/W image from the DMC2. The same applies when turning the UPPER DISPLAY potentiometer to OFF. This single display configuration is called: "MONO" display configuration (M). More generally, it corresponds to any situation with only one DU left for all the ECAM information display. Through the ECAM/ND XFR selector switch, the pilots can call the ECAM system image on their ND (in lieu of the ND image). Obviously, the pilots can at any time get their ND image back by setting the ECAM/ND XFR selector switch back to NORM. In the event of lower ECAM DU failure, the same as above applies: the Engine/Warning image remains displayed on the upper ECAM DU, but each pilot can call the ECAM system image on his ND if required by means of the ECAM/ND XFR selector switch. In the event of failure of both upper and lower ECAM DUs, there is no more ECAM image on display. Each pilot can recover the E/W image on his ND, by means of the ECAM/ND XFR selector switch. In this case, the pilot having the E/W image on his side can temporarily replace it by an A/C system/status image, by keeping the related key on the ECAM CP pressed.
 As long as an A/C system key or the STS key is held pressed, the corresponding page appears on the ND instead of the E/W image, but precautions are taken against the jamming of the key: after 3mn, the DU automatically displays the E/W image again.
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 31-60-00Page A9 1201-299, 301-302, 1Config-1 May 01/05 1 1 1CES 1 As soon as the pilot releases the key, the E/W image appears again. In case of complete failure of the ECAM CP, the ALL key enables the crew to select any A/C system page by means of successive actions on this key. In fact, the contacts of the ALL key are directly wired to the DMC for that purpose.

 (d) ECAM-ND transfer By means of the ECAM/ND XFR selector switch, each pilot can call on his ND an ECAM image (normally A/C system or status image, or Engine/ Warning image if both ECAM DUs are inoperative) instead of the ND image. Obviously, the pilots can at any time get their ND image back by setting the selector switch back to NORM.
 (3) Transmission between DMCs and DUs The transmission of data from the DMCs to the DUs (tele-loading of the drawing programs, and sending of the so-called dynamic data) is made through a digital bus. If a DU is selected for a different image (for instance, the ND having to display an ECAM image), the time delay before obtaining the new image, due to the tele-loading of the new image fixed data, does not exceed 500 ms. The DUs acknowledge proper reception of fixed and dynamic data and send to the DMCs through a digital bus (feedback link) status reports on the tele-loading and the drawing of the image, as well as information concerning the status and the proper operation of the DU itself (for instance, DU beam, DU temp, DU anomaly informations).
　
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